The Lemur That Was a Fish

A sketch of the "Arrhinolemur" skull - as seen from the top and the left side - from Florentino Ameghino's 1899 paper. At the time this drawing was made, the puzzling skull had only been partly cleaned.

Fossils are not always what they seem. Megarachne, once heralded as the largest spider of all time, was actually a sea scorpion. The squishy Cambrian critter Nectocaris has been transformed from one of our early chordate cousins to an enigmatic invertebrate of unknown affinity. Tracks thought to be left by an enormous hopping amphibian were later found to be scratch marks left by a giant, unknown invertebrate as it pulled itself along a Carboniferous shore. And, as I was reminded yesterday, there was the “lemur” that was a fish.

The demise of the muddled primate, formerly known as “Arrhinolemur” scalabrinii, isn’t news. Paleontologists have known about the mistake since 1945, and the paper that catapulted the story into the news yesterday has more to do with the specimen’s piscine identity than fossil misidentification. Still, beneath the obvious “How the hell did they mistake a fish for a lemur?” hook, there lie a pair of deeper stories about paleontological politics and fossil fishes.

As researchers Sergio Bogan, Brian Sidlauskas, and colleagues point out in their Neotropical Ichthyology study, the tale of “Arrhinolemur” goes back to 1898. In that year the pioneering Argentine paleontologist Florentino Ameghino named the creature on the basis of a skull given to him by colleague Pedro Scalabrini. The specimen was not fully cleaned of the encasing rock, but, despite being obscured, Ameghino believed that the skull represented an archaic lemur with almost no snout to speak of. The following year, after a little prep work, Ameghino reinforced his position and assigned the primate to its own order, the Arrhinolemuroidea.

But a lemur in South America made no sense. Modern lemurs have only been found on the island of Madagascar, off Africa’s southeastern coast. And even though lemur-like primates called adapiforms once clambered through dense forests over much of the northern hemisphere, they didn’t have any record at all in South America. Lemurs and their forebears had no known connection to South America. “Arrhinolemur” seemed to be a fossil fluke – a lemur that didn’t really resemble any other known species, entirely in the wrong place.

One of Ameghino’s admirers, American paleontologist George Gaylord Simpson, solved the puzzle in his huge 1945 monograph on mammal classification. Fossil experts had doubted Ameghino’s identification of “Arrhinolemur” for years and generally ignored the seven million year old specimen. When Simpson looked at the fossil himself, he found that “The one specimen in question is the crushed skull of a fish.” That’s why the primate made no anatomical or evolutionary sense. Ameghino’s “lemur” had nothing to do with primates.

In time, other researchers followed up on Simpson’s reinterpretation. Four decades later, Alvaro Mones identified the “Arrhinolemur” skull as a previously-unknown species of fossil fish possibly related to a freshwater group still alive today called the characids. Now Bogan and co-authors have closed the loop with a full redescription.

Mones was on the right track. The fish belonged to the anostomid lineage of the characiforms – the diverse group that contains piranhas, tetras, and kin – and represents a previously-unrecognized species within the genus Leporinus. Since Ameghino already gave the fossil a unique species name, and Leporinus was named decades before “Arrhinolemur“, the existing genus and species names were mashed together to create the new combination of Leporinus scalabrinii. All the paleontological paperwork has now fallen into place.

Yet there is one critical question that has been sidestepped in all the coverage this story has received so far. Why did Ameghino make what would seem to be such a boneheaded mistake? I e-mailed Oregon State University ichthyologist Brian Sidlauskas, one of the study’s co-authors, for his thoughts on the matter.

The skull of Leporinus scalabrinii (formerly “Arrhinolemur”), facing left. After full prepration, the fishy nature of the fossil is immediately clear. From Bogan et al., 2012.

“At least part of the answer is that most of the skull was still encased in matrix when Ameghino looked at it,” Sidlauskas wrote back, and explained that the fossil’s teeth “were the most visible part” of the specimen. This was a critical happenstance because “the teeth of the genus Leporinus (into which the fossil fits) are actually remarkably mammal-like (the genus name means ‘little rabbit’),” he noted, “So, the mammalian ID isn’t quite as crazy as it initially sounds.”

Calling a fish a primate is an embarrassing goof, especially since Ameghino later wrote a review of Argentina’s fossil fish, but Sidlauskas’ explanation sounds about right. It’s easy to misidentify an unprepared specimen that has confusing characteristics. But I have to wonder if Ameghino’s error wasn’t only an isolated case of mistaken identity, but part of a larger, idiosyncratic evolutionary hypothesis.

Along with his two brothers – Carlos and Juan – Florentino Ameghino was one of the most important founding figures in South American paleontology. Other researchers such as Charles Darwin had discovered fossils in Patagonia’s geologic formations before, but the Ameghino brothers were on a mission to develop paleontology within Argentina rather than let European and American scientists cart off the country’s prehistory. While Carlos was the field expert who built up a massive collection, and Juan helped run the bookstore that provided both income and workspace for research, Florentino was almost entirely a theorist who focused on interpreting what Carlos dug up. And, rather than follow what his peers in North America and Europe were saying about transmutation, Florentino developed a unique vision of South America as the critical cradle of evolutionary experimentation.

Many of the fossil mammals Carlos found didn’t fit into the classification schemes developed by other researchers. There were beasts that bore a superficial resemblance to horses and elephants, for example, but weren’t quite like known horses and elephants. Rather than cram these creatures into pre-existing patterns of evolution centered on the northern hemisphere, Florentino drew all mammal groups back to South America. Ultimately, ignoring the monotreme-marsupial-placental mammal split other naturalists drew on the basis of reproduction, Florentino drew the origins of all major mammal groups back to South American marsupials.

As Simpson later wrote in a short biography, “it can be said that for Florentino Ameghino all the mammals in the world had as their ultimate ancestor Patagonian ancestors of various sorts.” This included humans. In a move that pleased nationalists who justifiably wanted to promote Argentina is fertile ground for science, art, and culture, Florentino proposed that humans not only originated in South America, and added that apes were degenerate humans rather than primitive holdovers on closely related parts of our family tree.

(Florentino wasn’t alone in his pride. Other paleontologists were doing the same. During the late 19th and early 20th centuries, Darwin’s suggestion that the critical moments in human origins occurred in Africa were largely ignored for a variety of scientific, cultural, and racist reasons. Leading anthropologists looked to Europe and Asia for the earliest human ancestors.)

Along with other fossil primates he had named in 1891 – Homunculus patagonicus and “Anthropops perfectus” – Florentino’s “Arrhinolemur” would seem to make South America the primeval home of primates, too. Identifying a far-flung lemur would fit perfectly in Florentino’s frustrating research program of drawing all mammals back to his home country. Perhaps, combined for his penchant for identifying new species and genera on the slightest of differences, the nationalistic aspect of Florentino’s philosophy might explain why he saw a lemur in a fish.

I could be wrong, of course. As Sidlauskas said when I mentioned my hypothesis, “it is hard to know exactly what he was thinking 117 years ago.” “Arrhinolemur” fits Florentino’s research pattern, but we’ll never know whether it was an honest mistake or resulted from an effort to reinforce a foregone conclusion. By all accounts, Florentino was a brilliant, tenacious, iconoclastic, and highly-productive paleontologist, and finding the proper place of “Arrhinolemur” in his vast body of work is no simple task.

Finding the right context for the erstwhile primate in the media is a little simpler, but, nevertheless, fraught by the state of science news – when a big hook can overwhelm nuance. Simpson correctly identified that the skull belonged to a fish over six decades ago, so, while most people haven’t heard the story, the lemur-to-fish rebranding isn’ta novel discovery. Given this fact of the record, I asked Sidlauskas if he and his colleagues had gleaned anything unexpected through redescribingLeporinus scalabrinii. What story does the fish have to tell?

For years, “Arrhinolemur” was a hanging thread. No one doubted that the fossil was a fish skull, but, as Sidlauskas explained, “The trouble was that no one really knew what the fossil actually WAS.” The new paper finally gives the fish an official name and places it in evolutionary context. And even though the new analysis doesn’t really change anything for paleoprimatologists, the fish is a boon to ichthyologists. “This is the only articulated fossil of an anostomid fish known to exist; otherwise the fossil record for the family is just bone fragments and teeth,” Sidlauskas wrote. This more complete fossil confirms that “fishes much like part of the modern South American fauna were swimming around the region where Buenos Aires now occurs around 7 million years ago”, and this will help ichthyologists track the timing and patterns of evolution among similar fish. Leporinus scalabrinii isn’t quite like any living species, but its close enough to some modern fish to fit within a genus that’s still swimming around – a subtly distinct link to a time when Terror Birds and sabercats still roamed Argentina.

[Thanks to Anthony Hallam for tracking down Ameghino’s “Arrhinolemur” papers for me.]